The present invention is generally concerned with a process and apparatus for monitoring a condition of a tire, and more particularly with a process and apparatus for monitoring a condition of a pneumatic tire for diagnosing an impending failure thereof.
In order to transport bulk materials, such as coal, iron ore and other minerals, the mining industry uses Off-The-Road (OTR) vehicles that typically weigh up to 250 tons when fully loaded, with the result that exceedingly high internal stresses are imposed on the tires of such vehicles in the course of their daily use. Such internal stresses, which are primarily attributable to a number of factors including driving at excessive speeds, are so destructive of such tires that it is not uncommon to have to replace the tires. On the other hand, in order to maximize the productivity of OTR vehicles, they are normally driven as fast as possible until a user perceives that the internal physical condition of any given tire is marginal. Whereupon, the operator either stops, in the case of a loss of tire pressure, or reduces the speed of the vehicle, in the case of an excessive temperature condition, to relieve the internal stresses giving rise to the marginal condition, thereby prolonging the life of the tires. Thus the speed of an OTR vehicle is controlled on the basis of the operator""s perception of the condition of the tires at any given time. And, if the operator""s perception is erroneous, the productivity of the vehicle is unnecessarily reduced.
Accordingly, a long-standing need of the mining industry has been to ensure that the operators of OTR vehicles are provided with accurate information concerning various conditions of the tires of such vehicles, with a view to maximizing the productivity of the vehicles.
Various attempts have been made in the prior art to meet the aforesaid need, most recently by mounting integrated circuits within each of the tires of an OTR vehicle, for detecting respective conditions related to an imminent failure of each tire and providing the OTR vehicle operators with timely information concerning such conditions.
For example, U.S. Pat. No. 5,562,787, issued to Koch et al., disclosed a method and apparatus for monitoring respective conditions in the tires of vehicles. The apparatus comprises a monitoring device that is connectable to the interior of a tire and includes an integrated circuit having a transmitter. In addition, the monitoring device includes a plurality of sensors connected to the integrated circuit. The sensors continuously detect respective conditions of the tire and provide corresponding signals to the integrated circuit. The integrated circuit is programmed to periodically sample the tire condition signals, to compare the respective samples to respective standards, to generate respective tire condition signals based on the comparisons, and to provide an information signal to the operator of the vehicle when any tire condition signal is indicative of a marginal condition of the tire. In addition, the integrated circuit is programmed to be normally dormant but to transmit information signals concerning the then current tire condition signal to the operator in response to receiving a wake-up signal from the operator. Moreover, the integrated circuit may also be programmed to store data corresponding to periodic tire condition signals for historical, record keeping, purposes, and to cause the transmitter to transmit such historical data in response to receiving another wake-up signal.
As discussed in European Patent No. EP 0 936 089 A2, published Aug. 18, 1999, in order to avoid the stress, strain, impact and cyclic fatigue that such monitoring devices are ordinarily exposed to when mounted within a tire, the prior art integrated circuits along with the attached transmitter and sensors have been encapsulated in rigid or semi-rigid materials, such as urethanes, epoxies, polystyrene resins, hard rubber compounds, or the like. The encapsulations have then been assembled with a battery connected thereto. The resulting assembly, know in the prior art as an electronic tire tag, has then been wrapped with a green rubber material forming a housing therefor, and the housing has thereafter been added to the structural green rubber material forming a tire assembly and been vulcanized therewith for forming a cured tire. The cured tire thus includes an electronic tire tag embedded in the tire and forming a part thereof, and is discarded when the tire is discarded.
To provide for repair and replacement of such electronic tire tags, the aforesaid European Patent, which is assigned to the assignee of the aforesaid U.S. Patent, discloses a method and apparatus for removably mounting such tags within a tire. The apparatus includes a rubber patch, which may be vulcanized with the tire but is preferably separately vulcanized and attached to a vulcanized tire. The rubber patch includes a housing having a cavity formed therein. The cavity has a sidewall and is dimensioned for removably receiving therein the electronic tire tag. The electronic tag of the European Patent includes the above discussed structure of the U.S. Patent, including a transmitter, sensors and a battery, it being noted that the aforesaid U.S. Patent is incorporated by reference into, and made a part of, the European Patent. In addition, the European Patent calls for the optional inclusion of an antenna extending from the encapsulation. Assuming the provision of the antenna, opposed slots are formed in the sidewall of the housing for receiving the antenna when the tag is removably connected to the housing of the rubber patch. For retaining the tag in the housing, the housing and tag are respectively provided with compatible connecting means, such as the structures discussed in the European Patent, wherein the tag is either removably pinned, splined, threadably connected or interlocked to the housing.
Notwithstanding the aforesaid advancements of the prior art, the data provided to the operators of OTR vehicles, concerning the temperature conditions of the tires of such vehicles, continues to inaccurately reflect marginal conditions of the tires, due to various factors. For example, the practice of the prior art is to mount electronic tire tags centrally of the innerliner of a tire, in order to minimize the effects of stress, strain, impact vibration and cyclic fatigue imposed on the electronic tags. As a result, the monitoring devices sample tire temperatures at a location that is removed a considerable distance from the area of the tire where the temperature is most closely indicative of a marginal condition signaling an impending breakdown of the tire, that is, the temperature at the side edges of the belts, and thus near the shoulder portions of tires, where delaminations of the ply, belts and surrounding rubber materials occur due to the build up of internal stresses. In order to compensate for the difference between the sensed temperature and the temperature at such side edges, the prior art integrated circuits have algorithms that apply a scaling constant to the sensed temperature to calculate the temperature from the center of the innerliner to the vicinity of the shoulder portions of the tire. Unfortunately, the tire temperature at the center of the innerliner of a given tire may be significantly less than the temperature at shoulder portions of the tire, and change with different tire designs.
Accordingly, in addition to the problem of tag location, it has been found that the prior art algorithms inaccurately calculate the temperatures at the side edges of the belt, due to such calculations being based on adding a constant temperature factor to the temperature measured at the centerline of the tire to compensate for the distance that the temperature sampling sensor is spaced from the side edges of a belt. Since the location of the temperature sensors and such calculations result in providing erroneous information to the operators of OTR vehicles, the operators may prematurely reduce the speed of such vehicles. The consequent adverse effect on the productivity of such vehicles is costly to the mining industry.
According to the invention, there is disclosed a method of monitoring conditions of a pneumatic tire. The pneumatic tire comprises a central tread, one or more belt(s) disposed radially inwardly of the tread and an innerliner disposed radially inwardly of the belt. The belt(s) having a side edge. An electronic tag and associated condition sensors are disposed within the tire. The method includes the steps of sensing a first temperature which is the temperature of the tire innerliner adjacent to the belt edge with the electronic tag. A second temperature is sensed which is the air temperature within the tire with the electronic tag. Also, the air pressure within the tire is sensed with the electronic tag.
The sensing of the conditions is performed by sensing at a sequence of discrete time intervals. A value of one or more of the conditions sensed at an immediately previous time interval is compared to a current value of the one or more conditions. At a current time interval, the process includes the step of determining whether select one or more of the conditions has changed by a threshold amount since an immediately previous time interval.
The select one or more conditions is either or both of the first and second temperatures and the threshold amount is plus or minus two degrees centigrade. Further, the select one or more conditions is the air pressure within the tire and the threshold amount is plus or minus two pounds per square inch.
Also according to the method, the electronic tag can be disposed adjacent a shoulder portion of the tire and/or at an area of the innerliner where the tire is thickest. The electronic tag can also be disposed at an area of the innerliner where the tire is least able to dissipate heat or at an area of the innerliner where the temperature samples are the most closely related to determining whether or not an internal breakdown of the tire is imminent.
Also according to the invention, there is disclosed a method of monitoring at least one condition of a pneumatic tire (10), the pneumatic tire by disposing an electronic tag within the tire adjacent a shoulder portion of the tire. The at least one condition is selected from the group consisting of a first temperature which is the temperature of the tire innerliner adjacent to the belt side edge, a second temperature which is the air temperature within the tire; and air pressure within the tire. The sensing the at least one condition is by performing sensing at a sequence of discrete time intervals. Also the method includes comparing a value of the at least one condition sensed at an immediately previous time interval to a current the value of the at least one condition. The steps include at a current time interval, determining whether the at least one condition has changed by a threshold amount since an immediately previous time interval.